An optical isolator is an optical component designed to allow a beam of light to pass through the component in a principle direction, and to prevent a beam of light from passing through the component in the opposite of the principle direction. Optical isolators may be used, for example, to prevent laser diode self-oscillation (i.e., prevent feedback from entering a laser cavity).
FIG. 1 is a block diagram of a prior art of an integrated optical isolator. In this illustration, optical isolator 100 is shown to include TE polarizers 130 and 135, quarter wave-plate 140 and non-reciprocal polarization rotator 150. Operation of isolator 100 is shown via light 110 and 120.
Light 110 is shown as traveling in the principle direction. The principle direction may be the direction of light that exits a laser cavity (not shown). In this example, light 110 comprises TE polarized light (i.e., s-polarized light), and this light passes through TE polarizer 130 (shown as light state 111). Said light is rotated by non-reciprocal rotator 150 45° with a right-hand screw motion (shown as light state 112), and subsequently rotated by quarter wave-plate 140 45° with a left-hand screw motion (shown as light state 113); thus, light 110 is still TE polarized light at this state. Light 110 passes through TE polarizer 135 and out of optical isolator 100 (shown as light state 114).
Light 120 is shown as traveling through optical isolator 100 in the opposite of the principle direction. In this example, light 120 is TE polarized light, and this light passes through TE polarizer 135 (shown as light state 121). Said light is rotated by quarter wave-plate 140 45° with a left-hand screw motion (shown as light state 122), and is subsequently rotated by non-reciprocal rotator 150 45° with a left-hand screw motion again (shown as light state 123); thus light 170 has been rotated to be TM polarized light (i.e., p-polarized light). This light is blocked by TE polarizer 130. Thus, optical isolator 100 has prevented light 120 from traversing the optical isolator in the opposite of the principle direction.
The above described prior art solution requires discrete optical components 130, 135, 140 and 150 that are relatively large compared to the other integrated photonic components. Furthermore, the addition of these discrete optical components requires cutting through substrate 190 and aligning these prefabricated components one at a time, increasing manufacturing complexity.
Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein. An overview of embodiments of the invention is provided below, followed by a more detailed description with reference to the drawings.